Limits to the flux of ultra-high-energy cosmic rays from exotic phenomena in the galactic halo

A detailed analysis is made of the likelihood of extragalactic cosmic-ray p articles above 10(19) eV having come from the decay of dark-matter particle s or neutrino-neutrino annihilations in the galactic halo. Even if we accep t the most optimistic assumptions it is difficult to account for more than about 50% of the observed intensity having been produced by the decay of da rk-matter particles: the preferred model with a one-standard-deviation limi t gives a figure of only 15%. Fur neutrino-neutrino annihilations the corre sponding value is about 20%.